TOUCH-SCREEN voting machines have their problems, as a team of UC computer-security experts showed last month. Secretary of State Debra Bowen, however, the state's top voting official, overreacted to the still-incomplete evidence at hand.

In a confused, last-minute ruling, she has effectively banned the ATM-like devices used by nearly a third of the 50 states. Her ruling came at near-midnight on the last possible day, leaving registrars in the lurch as they prepare for a statewide primary in six months.

In the voting world, Bowen's order leaves barely enough time for registrars to prepare because other machines - most likely optical-scan devices that read marked-up paper ballots - must be found and staffs trained. Long lines are predicted, and extra money must be found. The San Diego County registrar, one of many steaming-mad local voting officials, is thinking of sending out a million postcards urging absentee voting to avoid a polling-place traffic jam.

Bowen, an avowed critic of touch-screens, could have handled it better. Instead, she's inviting election-day chaos unless a workable compromise is arranged.

At best, she has demonstrated a barely plausible scenario that touch-screens can be hacked as diehard critics have worried about for years. But the UC study allowed experts full access to the machines and computer manuals, doubtful conditions in real-world precincts. The inquiry provides useful pointers to equipment makers who should improve their products, but the results don't justify her decertification of vote-counting systems that have operated without incident.

In the swirl of doubts about ballot security, voters need guidance and common sense. Unfortunately, Bowen's ruling offered neither.